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Why do I have a fever?


Fever is a natural reaction of the body. The increase in temperature is not caused by external aggression but by our own immune system which is trying to defend itself against this aggression.

Fever results from a disorder of the thermoregulatory center.

Our brain has a thermoregulatory center that works like an internal thermostat . A thermostat is a device that keeps a system at a relatively stable  temperature . The desired temperature is set and when there are too pronounced deviations from this desired temperature, mechanisms are triggered in order to maintain the desired temperature.

In the body, the thermostat or thermoregulatory center is located in the hypothalamus, an area with specific functions in the brain.

  • The hypothalamus is a structure of the central nervous system, located in the encephalon (part of the brain), which is among other things responsible for making the connection between the nervous system and the endocrine system.

  • In this way, the hypothalamus is responsible for several metabolic processes and other activities of the autonomic nervous system. (The autonomic nervous system (also called visceral nervous system or vegetative nervous system) is the part of the nervous system responsible for functions not subject to voluntary control)

  • One of the functions of the hypothalamus is thermoregulation.

  • It can be seen as a “thermostat”

    • Normally the body thermostat is set to +/- 37°

    • In fever, everything happens as if the hypothalamic thermostat was set for a reference temperature above 37°C.

  • Disturbances in the reference temperature of the hypothalamic thermostat arise from the action of pyrogenic substances. (substances that increase body temperature) These pyrogenic substances induce an overproduction of certain “prostaglandins” in the hypothalamus. This puts the reference temperature at another level and the fever appears.


When inflamed, the hypothalamus releases substances that regulate the immune mechanism. Fever is one of the consequences.

Although fever is unpleasant, it has in many cases a useful role:

  • Many pathogens, such as bacteria and viruses, are not resistant to high temperatures.

  • Fever spikes keep your defense mechanism working until the germs are fought off.

Fever is therefore a common symptom of illness. It is particularly common with colds, throat and/or ear infections, and flu. Feeling hot, chills, headache, flu-like feeling, weakness and lethargy are just some of the symptoms associated with fever. Fortunately, not all fever flares require a trip to the doctor.

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